The invention relates to adjust extraction installation for blast furnace gas.
Dust extraction installations for blast furnace gas generally comprise a preliminary cleaning stage and a fine cleaning stage. The preliminary cleaning stage is formed by a dust catcher. The latter consists essentially of a large vertical pressure vessel, which is connected to the blast furnace throat via a gas pipe with a large cross-section. The gas enters the pressure vessel vertically from the gas pipe, wherein the increase in cross-section on entry of the gas into the pressure vessel results in a considerable reduction of its velocity. Consequently at least the coarsest particles fall vertically from the gas flow before the flow leaves the dust catcher at the top end of the pressure vessel after reversal of direction. The separated particles are collected in a dust hopper, from which they are removed via a lock, at the bottom end of the pressure vessel. The pre-cleaned blast furnace gas then passes from the dust catcher to the fine cleaning stage, which normally comprises at least one gas scrubber or electrostatic precipitator.
As the dust catcher achieves poor separation efficiency, the blast furnace gas can also be passed through a cyclone separator after leaving the dust catcher and before being passed to the fine cleaning stage. A cyclone separator of this type comprises one or more cyclones connected in parallel. The latter are pressure vessels, into which the blast furnace gas is fed tangentially at high speed, with the result that it is set into a swirling motion. The particles are thrown by centrifugal force to the outer wall of the cyclone separator and slide down this outer wall into a dust hopper. It is obvious that two-stage preliminary cleaning of this type significantly increases the costs of the dust extraction installation and requires expensive piping on the gas side for the connection of the cyclone separators connected in parallel.
A dust extraction installation for blast furnace gas in which the dust catcher is replaced by a single large cyclone separator has likewise already been built (dust extraction installation of blast furnace No. 2 in the Schwelgen works of THYSSEN Krupp Stahl AG). The main gas pipe from the blast furnace is introduced tangentially into the cyclone vessel, with the result that the blast furnace gas is set into a swirling motion, so that the dust separation takes place as already described above. However, a large cyclone separator of this type has so far been unable to displace the familiar dust catcher from the market, although there has long been a requirement for more efficient preliminary cleaning of the blast furnace gas. The chief reasons are most probably: (1) problematical connection of the gas pipe from the blast furnace throat to the large cyclone separator; (2) reservations about wear on the pressure vessel and (3) a lack of empirical values concerning the use of such large cyclone separators for the preliminary cleaning of blast furnace gases. With regard to (1) it should be stated that the tangential connection of the large blast furnace gas pipe (with a cross-section up to 4 m) to the cyclone vessel requires inter alia a complicated pipe route, lateral supporting structures requiring a lot of space, additional pipe bends and compensators and expensive rectangular ducts, which are reinforced against buckling. If an existing dust catcher is to be replaced by a large cyclone separator, this necessitates important modifications to the blast furnace gas pipe and steel construction. There is often insufficient space for lateral supporting structures for the gas pipe from the blast furnace throat. In this connection it should likewise be pointed out that the support of the gas pipe from the blast furnace throat is by no means unproblematical due to the heavy weight of the pipe (heavy refractory lining), the wind load to be taken into account (large diameter) and the thermal expansion (large length and large temperature differences). With regard to (2) it should be noted by way of explanation that the gas flowing into the cyclone separator impinges frontally at high speed on the vessel wall, which leads to heavy wear. With regard to (3) it should be mentioned that the blast furnace operators fear inter alia that the predicted separation characteristics of the large cyclone separator will not be observed. As the separation characteristics of a cyclone separator of this type are determined exclusively by the geometry of the cyclone separator and the tangential gas inflow, it will be appreciated that subsequent improvement of the separation characteristics is possible only at considerable cost.
Therefore, the problem underlying the present invention is to provide a dust extraction installation for blast furnace gas with a preliminary cleaning stage, which has a high separation efficiency but does not have the above-mentioned disadvantages of the known solution with a large cyclone separator as the preliminary cleaning stage, or has these disadvantages only to a reduced extent.
According to the invention this problem is solved by a dust extraction installation according to claim 1. A dust extraction installation of this type comprises, in a known manner, a preliminary cleaning stage and a fine cleaning stage. The preliminary cleaning stage is formed by a large cyclone separator, which comprises a vertical pressure vessel, into which a gas pipe from the blast furnace terminates. According to the invention an axial feed device for the blast furnace gas, to which the gas pipe from the blast furnace can be connected, is provided at the top end of the pressure vessel. This axial feed device is designed in such a way that it introduces the blast furnace gas into the pressure vessel in an axial direction. A swirl device with guide blades is arranged under the feed device. It is designed in such a way that it causes the blast furnace gas introduced axially into the pressure vessel to swirl about the axis of the pressure vessel. The particles present in the blast furnace gas are thrown by the centrifugal force to an outer wall of the pressure vessel and slide down this wall. It should be stated that the axial feed device for the blast furnace gas, compared to a tangential feed device, substantially simplifies the connection of the large cyclone separator to the gas pipe from the blast furnace. The pipe can be connected from above to the axial feed device and thus be supported vertically above the cyclone separator. Consequently the not insignificant support problem is greatly simplified. Separate supporting structures, additional pipe bends and compensators as well as rectangular ducts reinforced against buckling for a lateral tangential connection of the pressure vessel are dispensed with. Furthermore, the wear on the vessel wall in the inflow area is greatly reduced by the axial introduction of the blast furnace gas. The swirling motion of the blast furnace gas is produced by the guide blades, which can be designed as easily interchangeable wearing parts. The dust extraction installation according to the invention thus has the additional advantage that the separation characteristics of the installation can be adapted at any time to new requirements by modifications to the guide blades in the swirling device, i.e. at acceptable cost.
The pre-cleaned blast furnace gas could be removed, for example, at the bottom end of the cyclone separator by a central outlet connection pipe. As in most cases the blast furnace gas enters the following fine cleaning stage from above, it is however advantageous to remove the pre-cleaned blast furnace gas at the top end of the pressure vessel through a central outlet connection pipe. In this case the feed device advantageously has at least two inlet connection pipes aligned upward, which terminate in the pressure vessel around the central outlet connection pipe. The greater the number of inlet connection pipes in the feed device, the more homogeneous is the inflow to the swirling device in the pressure vessel. For the connection to the blast furnace gas pipe the feed device advantageously has a distributor outside the pressure vessel. This distributor comprises a connection pipe aligned vertically upwards and pipe branches aligned downwards. The gas pipe from the blast furnace is connected to the central connection pipe and the inlet connection pipes of the feed device to the pipe branches. Hence the fine cleaning stage can be connected to the central outlet connection pipe of the pressure vessel by means of a connecting line, which is led between two adjacent pipe branches of the distributor. The distributor is preferably designed with axial symmetry.
In the pressure vessel the feed device advantageously has a tapered inlet bell extending downwards, which is traversed by the central outlet connection pipe. An annular gap, in which the swirling device is installed, is formed between the bottom edge of the inlet bell and the wall of the pressure vessel. This inlet bell is advantageously supported by the central outlet connection pipe, so that the pressure vessel and inlet bell can expand independently of each other.
The guide blades are advantageously inserted from outside through slits in the wall of the pressure vessel into the swirling device, so that they can be changed relatively easily. In an advantageous embodiment each of the guide blades has at its outer end a mounting plate, which is screwed with a seal on to a flange which encloses the corresponding slit in the wall of the pressure vessel. The inner end of a guide blade can be introduced into a slit-type recess in the bottom edge of the inlet bell in order to keep the gas flow passing the swirling device as small as possible.